1. Field of the Invention
The present invention relates to a spin-valve magnetoresistive thin film element which changes in electric resistance according to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic fields. More particularly, the present invention relates to a spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is divided into two layers, such that the magnetization (Ferri-state) between the two pinned magnetic layers can be maintained in a thermally stabilized state. The present invention also relates to a thin film magnetic head using this spin-valve magnetoresistive thin film.
The present invention also relates to a spin-valve magnetoresistive thin film element which changes in electric resistance according to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic fields, and particularly relates to a spin-valve magnetoresistive thin film element wherein the magnetization of the pinned magnetic layer can be maintained in a more stabilized state by causing a sensing current to flow in an appropriate direction, and also relates to a thin film magnetic head using this spin-valve magnetoresistive thin film element.
The present invention also relates to a spin-valve magnetoresistive thin film element which changes in electric resistance according to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic fields, and particularly relates to a method for manufacturing a spin-valve magnetoresistive thin film element wherein magnetization control of the pinned magnetic layer can be performed in an appropriate manner of appropriately adjusting the magnetic moment of the pinned magnetic layer, and the direction and size of the magnetic field to be applied during thermal treatment, and also relates to a method for manufacturing a thin film magnetic head using this spin-valve magnetoresistive thin film element.
2. Description of the Related Art
A spin-valve magnetoresistive thin film element is a type of GMR (giant magnetoresistive) element which makes use of the giant magneto resistance effect, and is used for detecting recorded magnetic fields from recording mediums such as hard disks and the like.
The spin-valve magnetoresistive thin film element has several advantages, such as having a relatively simple structure for a GMR element. Further, the spin-valve magnetoresistive thin film element can change resistance under weak magnetic fields.
In its simplest form, the spin-valve magnetoresistive thin film element is comprised of an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically conductive layer, and a free magnetic layer. FIG. 28 is a cross-sectional view of a known spin-valve magnetoresistive thin film element, viewed from the side opposing a recording medium.
Also, FIG. 29 is a sideways cross-sectional diagram schematically illustrating the spin-valve magnetoresistive thin film element shown in FIG. 28.
Reference numeral 1 denotes a base layer formed of Ta (tantalum) for example, and formed on this base layer 1 is formed an antiferromagnetic layer 2, and further a pinned magnetic layer 3 is formed on the antiferromagnetic layer 2.
The pinned magnetic layer 3 is formed in contact with the antiferromagnetic layer 2, thereby generating an exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface between the pinned magnetic layer 3 and the antiferromagnetic layer 2, and the magnetization of the pinned magnetic layer is pinned in the Y direction in the Figure, for example.
Formed upon the pinned magnetic layer 3 is a nonmagnetic electrically conductive layer 4 formed of Cu or the like, and further formed upon the nonmagnetic electrically conductive layer 4 is a free magnetic layer 5. Formed on either side of the free magnetic layer 5 are hard magnetic bias layers 6 formed of a Coxe2x80x94Pt (cobalt-platinum) alloy for example, and the hard magnetic bias layers 6 are magnetized in the direction X in the Figure, so the magnetization of the free magnetic layer 5 is aligned in the direction X in the Figure. Accordingly, the fluctuation magnetization of the free magnetic layer 5 and the pinned magnetization of the pinned magnetic layer 3 are in an intersecting relationship. Incidentally, reference numeral 7 denotes a protective layer formed of Ta or the like, and reference numeral 8 denotes a lead layer formed of Cu or the like.
With this spin-valve magnetoresistive thin film element, a sensing current flows from the lead layer 8 either in the direction of X shown in the Figure or in the direction opposite to X shown in the Figure, with mainly the nonmagnetic electrically conductive layer 4 as the center. Then, when the magnetization of the free magnetic layer 5 aligned in the direction X in the Figure fluctuates due to magnetic field leaking from the recording medium (such as a hard disk), electric resistance changes according to the relationship between the magnetization of the free magnetic layer 5 and the magnetization of the pinned magnetic layer 3 pinned in the direction Y in the Figure, and a magnetic field leaking from the recording medium is detected by voltage change based on the change in the electric resistance values.
Also, with known arrangements, FeMn alloys, NiO, NiMn alloys, etc., are used for the antiferromagnetic layer 2. Of these examples, using FeMn alloys or NiO as the antiferromagnetic material does not necessitate thermal treatment in order to generate an exchange coupling magnetic field at the interface between the antiferromagnetic layer 2 and the pinned magnetic layer 3, but using NiMn as the antiferromagnetic material does necessitate thermal treatment.
Now, with known arrangements, NiMn alloys, FeMn alloys, NiO, etc., are used as antiferromagnetic materials for the antiferromagnetic layer 2.
However, of these, the blocking temperature of FeMn alloys and NiO alloys in particular is 200xc2x0 C. or lower, meaning that these materials are lacking in stability.
Particularly, in recent years, the number of revolutions of the recording medium and the amount of sensing current flowing from the lead layer 8 have been increasing, and the environmental temperature within the device reaches high temperatures of 200xc2x0 C. for example, or higher. Accordingly, using an antiferromagnetic material with low blocking temperature as the antiferromagnetic layer 2 of the spin-valve magnetoresistive thin film element reduces the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the antiferromagnetic layer 2 and the pinned magnetic layer 3. The result is that the magnetization of the pinned magnetic layer 3 cannot be appropriately pinned in the direction Y in the Figure, consequently allowing xcex94MR (rate of change of resistance) to drop.
The blocking temperature is determined solely by the antiferromagnetic material comprising the antiferromagnetic layer 2. Thus, even if the structure of the spin-valve magnetoresistive thin film element is improved, the blocking temperature itself cannot be raised.
For example, U.S. Pat. No. 5,701,223 discloses an invention wherein the structure of the pinned magnetic layer is improved and the exchange coupling magnetic field can be improved. However, this invention uses NiO as the antiferromagnetic layer, so the blocking temperature is around 200xc2x0 C. Thus, even though the exchange coupling magnetic field may be increased at room temperature, the exchange coupling magnetic field of the spin-valve magnetoresistive thin film element becomes smaller while the recording medium is running as the environmental temperature within the device reaches the vicinity of 200xc2x0 C. or higher. The exchange coupling magnetic field may becomes 0, so no xcex94MR can be obtained at all.
On the other hand, NiMn alloys have higher blocking temperatures than NiO or FeMn alloys, but the properties of these alloys such as corrosion-resistance and the like are poor, so an antiferromagnetic material with even higher blocking temperatures and excellent properties thereof such as corrosion-resistance is being demanded.
Also, as described above, the sensing current flows from the lead layer 8 with mainly the nonmagnetic electrically conductive layer 4 having low ratio resistance as the center, so a sensing current magnetic field is formed by the corkscrew rule because of the sensing current that is caused to flow. This sensing current magnetic field affecting the pinned magnetization of the pinned magnetic layer 3.
For example, as shown in FIG. 29, the magnetization of the pinned magnetic layer 3 is directed in the direction of Y in the Figure. But, if the sensing current magnetic field generated by causing sensing current to flow is directed in the direction opposite to Y in the Figure at the portion of the pinned magnetic layer 3, the direction of the pinned magnetization of the pinned magnetic layer 3 and the direction of the sensing current magnetic field do not match, so the pinned magnetization is affected by the sensing current magnetic field and wavers. This is a problem in that the state of magnetization becomes unstable.
Particularly, if an antiferromagnetic material such as an NiO or FeMn alloy which produces only a small exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the pinned magnetic layer 3 and the antiferromagnetic layer 2, and which has low blocking temperature, is used for the antiferromagnetic layer 2, the deterioration of the pinned magnetism at the pinned magnetic layer 3 is marked if the pinned magnetization direction of the pinned magnetic layer 3 and sensing current magnetic field direction are facing opposite directions, and destruction may occur such as the inversion of pinned magnetism.
In recent years, there is a trend to use a large sensing current in order to deal with higher densities. However, it is known that causing a sensing current of 1 mA to flow generates a sensing current magnetic field of approximately 30 (Oe), and further that the element temperature rises by about 150xc2x0 C. Thus, if several tens of mA of the sensing current is caused to flow, this will result in a sudden rise in the temperature of the element, and generate a massive sensing current magnetic field. Accordingly, in order to improve the thermal stability of the pinned magnetization of the pinned magnetic layer 3, an antiferromagnetic material with a high blocking temperature and which produces a large exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface between the pinned magnetic layer 3 and the antiferromagnetic layer 2 needs to be selected, and the sensing current needs to be directed in an appropriate direction so the magnetization of the pinned magnetic layer 3 is not destroyed by the sensing current magnetic field.
U.S. Pat. No. 5,701,223 discloses an invention wherein the pinned magnetic layer is divided into two layers and the magnetization of the two pinned magnetic layers is in an antiparallel state, whereby a large exchange coupling magnetic field can be obtained.
However, the antiferromagnetic layer disclosed here is NiO, and NiO has a low blocking temperature of around 200xc2x0 C., and only a small exchange coupling magnetic field (exchange anisotropic magnetic field) is generated at the interface between the pinned magnetic layer and the antiferromagnetic layer.
Particularly, in recent years, there is a trend to increase the rotating speed of the recording medium and increase the sensing current in order to deal with higher densities, which causes the environmental temperature within the device to rise. Thus, if NiO is used for the antiferromagnetic layer, the exchange coupling magnetic field is smaller, meaning that it is difficult to appropriately carry out magnetization control of the pinned magnetic layer.
On the other hand, NiMn alloys have a higher blocking temperature than the NiO, and the exchange coupling magnetic field (exchange anisotropic magnetic field) is also greater. Also, Xxe2x80x94Mn alloys (wherein X is Pt, Pd, Ir, Rh, Ru) using elements of the platinum group have come into focus as an antiferromagnetic material which has blocking temperature around that of NiMn alloys, a large exchange coupling magnetic field, and corrosion-resistance far better than NiMn alloys.
Employing such Xxe2x80x94Mn alloys using elements of the platinum group as the antiferromagnetic layer, and further dividing the pinned magnetic layer into two layers should facilitate the obtaining a greater exchange coupling magnetic field as compared to using NiO for the antiferromagnetic layer.
Presently, such Xxe2x80x94Mn alloys using elements of the platinum group need to be annealed in a magnetic field (thermal treatment) following formation of the film, in order to generate an exchange coupling magnetic field at the interface between the pinned magnetic layer and the antiferromagnetic layer, as is true with the case of NiMn alloys, as well.
However, unless the size and direction of the magnetic field applied during the thermal treatment, and the magnetic moment (saturation magnetization Msxe2x80xa2film thickness t) of the two divided pinned magnetic layers are appropriately adjusted, the magnetization of the two divided pinned magnetic layers cannot be pinned in a stable antiparallel state. Also, particularly, with so-called dual spin-valve magnetoresistive thin film elements (wherein the pinned magnetic layers are formed above and below the free magnetic layer with the free magnetic layer as the center thereof), the magnetization direction of the two pinned magnetic layers formed above and below the free magnetic layer must be appropriately controlled, or xcex94MR (the rate of resistance change) drops, causing problems such that only a small reproduction output can be obtained.
The present invention has been made in order to solve the above-described problems with the known art, and accordingly, it is an object of a first aspect of the present invention to provide a spin-valve magnetoresistive thin film element and a thin film magnetic head using this spin-valve magnetoresistive thin film element that is thermally stable and capable of increasing the exchange coupling magnetic field, by improving the structure of the pinned magnetic layer and the material comprising the antiferromagnetic layer in particular, and further appropriately adjusting the film thickness of the pinned magnetic layer.
Similarly, it is an object of a second aspect of the present invention to provide a spin-valve magnetoresistive thin film element and a thin film magnetic head using this spin-valve magnetoresistive thin film element that is capable of maintaining the magnetization state of the pinned magnetic layer in a thermally stable manner, by improving the structure of the pinned magnetic layer and the material comprising the antiferromagnetic layer in particular, and further controlling the direction in which the sensing current is caused to flow in an appropriate direction.
Also, it is an object of a third aspect of the present invention to provide a method for manufacturing a spin-valve magnetoresistive thin film element and a thin film magnetic head using this spin-valve magnetoresistive thin film element that is capable of maintaining the magnetization of two pinned magnetic layers in a stable antiparallel state, by appropriately controlling the magnetism moment of a pinned magnetic layer which has been divided into two layers, and the direction and size of a magnetic field applied during thermal treatment, and further capable of obtaining high xcex94MR around that of known arrangements.
To this end, a first aspect of the present invention provides a spin-valve magnetoresistive thin film element, comprising: an antiferromagnetic layer; a pinned magnetic layer formed in a manner contacting the antiferromagnetic layer, wherein the magnetizing direction is pinned by the exchange coupling magnetic field between the pinned magnetic layer and the antiferromagnetic layer; and a nonmagnetic electrically conductive layer formed between a free magnetic layer and the pinned magnetic layer. The magnetizing direction of the free magnetic layer is aligned so as to intersect with the magnetizing direction of the pinned magnetic layer. The pinned magnetic layer is divided into two layers with a nonmagnetic intermediate layer introduced therebetween. Here, with the pinned magnetic layer which comes in contact with the antiferromagnetic layer as a first pinned magnetic layer and with the pinned magnetic layer which comes in contact with the nonmagnetic electrically conductive layer as a second pinned magnetic layer, (the film thickness of the first pinned magnetic layer)/(the film thickness of the second pinned magnetic layer) is in a range of 0.33 to 0.95 or 1.05 to 4.
According to the present invention, (the film thickness of the first pinned magnetic layer)/(the film thickness of the second pinned magnetic layer) is preferably in a range of 0.53 to 0.95 or 1.05 to 1.8.
Also, according to the present invention, it is preferable that the film thickness of the first pinned magnetic layer and the film thickness of the second pinned magnetic layer are both in a range of 10 to 70 xc3xa4ngstrxc3x6m, and that |the film thickness of the first pinned magnetic layer minus the film thickness of the second pinned magnetic layer|xe2x89xa72 xc3xa4ngstrxc3x6m.
Further, with the present invention, it is even more preferable that the film thickness of the first pinned magnetic layer and the film thickness of the second pinned magnetic layer are both in a range of 10 to 50 xc3xa4ngstrxc3x6m, and that |the film thickness of the first pinned magnetic layer minus the film thickness of the second pinned magnetic layer|xe2x89xa72 xc3xa4ngstrxc3x6m.
Also, with the present invention, the free magnetic layer may be divided into two layers with a nonmagnetic intermediate layer introduced therebetween.
According to the present invention, the spin-valve magnetoresistive thin film element may comprise a single spin-valve magnetoresistive thin film element consisting of one layer each of the antiferromagnetic layer, first pinned magnetic layer, nonmagnetic intermediate layer, second pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer.
If the free magnetic layer divided into two layers, the free magnetic layer is formed to the side coming into contact with the nonmagnetic electrically conductive layer serves as a first free magnetic layer and the other free magnetic layer as a second free magnetic layer.
If the spin-valve magnetoresistive thin film element is a dual spin-valve magnetoresistive thin film element comprising: nonmagnetic electrically conductive layers formed above and below with the free magnetic layer as the center; the three layers of the second pinned magnetic layer/nonmagnetic intermediate layer/first pinned magnetic layer formed above one of the nonmagnetic electrically conductive layer and below the other nonmagnetic electrically conductive layer; and antiferromagnetic layers formed above one of the first pinned magnetic layers and below the other first pinned magnetic layer; wherein, of the free magnetic layer divided into two layers, one free magnetic layer serves as a first free magnetic layer and the other free magnetic layer as a second free magnetic layer.
In this aspect of the invention, the value of (the film thickness of the first free magnetic layer/the film thickness of the second free magnetic layer) is preferably in a range of 0.56 to 0.83 or 1.25 to 5, and more preferably in a range of 0.61 to 0.83 or 1.25 to 2.1.
Also, the present invention provides a spin-valve magnetoresistive thin film element, comprising: an antiferromagnetic layer; a pinned magnetic layer formed in a manner contacting the antiferromagnetic layer. The magnetizing direction is pinned by the exchange coupling magnetic field between the pinned magnetic layer and the antiferromagnetic layer by means of thermal treatment in a magnetic field. A nonmagnetic electrically conductive layer is formed between a free magnetic layer and the pinned magnetic layer. The magnetizing direction of the free magnetic layer is aligned so as to intersect with the magnetizing direction of the pinned magnetic layer. The pinned magnetic layer is divided into two layers with a nonmagnetic intermediate layer introduced therebetween. Here, with the pinned magnetic layer which comes in contact with the antiferromagnetic layer as a first pinned magnetic layer and with the pinned magnetic layer which comes in contact with the nonmagnetic electrically conductive layer as a second pinned magnetic layer, and with the product of saturation magnetization Ms and film thickness t as the magnetic film thickness (magnetic moment), (the magnetic film thickness of the first pinned magnetic layer)/(the magnetic film thickness of the second pinned magnetic layer) is in a range of 0.33 to 0.95 or 1.05 to 4.
With the present invention, it is preferable that (the magnetic film thickness of the first pinned magnetic layer)/(the magnetic film thickness of the second pinned magnetic layer) be in a range of 0.53 to 0.95 or 1.05 to 1.8.
Also, with the present invention, it is preferable that the magnetic film thickness of the first pinned magnetic layer and the magnetic film thickness of the second pinned magnetic layer are both in a range of 10 to 70 (xc3xa4ngstrxc3x6m tesla), and that |the magnetic film thickness of the first pinned magnetic layer minus the magnetic film thickness of the second pinned magnetic layer|xe2x89xa72 (xc3xa4ngstrxc3x6m tesla).
Further, with the present invention, it is even more preferable that the film thickness of the first pinned magnetic layer and the film thickness of the second pinned magnetic layer are both in a range of 10 to 50 (xc3xa4ngstrxc3x6m tesla), and that |the magnetic film thickness of the first pinned magnetic layer minus the magnetic film thickness of the second pinned magnetic layer|xe2x89xa72 (xc3xa4ngstrxc3x6m tesla).
Also, with the present invention, the free magnetic layer may be divided into two layers with a nonmagnetic intermediate layer introduced therebetween.
According to the present invention, the spin-valve magnetoresistive thin film element may comprise a single spin-valve magnetoresistive thin film element consisting of one layer each of the antiferromagnetic layer, first pinned magnetic layer, nonmagnetic intermediate layer, second pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer.
If the free magnetic layer divided into two layers, the free magnetic layer formed to the side coming into contact with the nonmagnetic electrically conductive layer serves as a first free magnetic layer and the other free magnetic layer as a second free magnetic layer.
If the spin-valve magnetoresistive thin film element is a dual spin-valve magnetoresistive thin film element comprising: nonmagnetic electrically conductive layers formed above and below with the free magnetic layer as the center; the three layers of the second pinned magnetic layer/nonmagnetic intermediate layer/first pinned magnetic layer formed above one of the nonmagnetic electrically conductive layer and below the other nonmagnetic electrically conductive layer; and antiferromagnetic layers formed above one of the first pinned magnetic layers and below the other first pinned magnetic layer; wherein, of the free magnetic layer divided into two layers, one free magnetic layer serves as a first free magnetic layer and the other free magnetic layer as a second free magnetic layer.
In this aspect of the invention, the value of (the magnetic film thickness of the first free magnetic layer/the magnetic film thickness of the second free magnetic layer) is preferably in a range of 0.56 to 0.83 or 1.25 to 5, and more preferably in a range of 0.61 to 0.83 or 1.25 to 2.1.
Also, with the present invention, it is preferable that the nonmagnetic intermediate layer introduced between the first pinned magnetic layer and second pinned magnetic layer be formed of one of the following, or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu.
Further, with the present invention, the spin-valve magnetoresistive thin film element may comprise an antiferromagnetic layer below the free magnetic layer, and in this arrangement, it is preferable that the thickness of the nonmagnetic intermediate layer introduced between the first pinned magnetic layer formed so as to come in contact with the antiferromagnetic layer and the second pinned magnetic layer formed so as to come in contact with the nonmagnetic electrically conductive layer be in a range of 3.6 to 9.6 xc3xa4ngstrxc3x6m, or more preferably, in a range of 4.0 to 9.4 xc3xa4ngstrxc3x6m.
Or, the spin-valve magnetoresistive thin film element may comprise an antiferromagnetic layer above the free magnetic layer, and in this arrangement, it is preferable that the thickness of the nonmagnetic intermediate layer introduced between the first pinned magnetic layer formed so as to come in contact with the antiferromagnetic layer and the second pinned magnetic layer formed so as to come in contact with the nonmagnetic electrically conductive layer be in a range of 2.5 to 6.4 xc3xa4ngstrxc3x6m or 6.6 to 10.7 xc3xa4ngstrxc3x6m, or more preferably, in a range of 2.8 to 6.2 xc3xa4ngstrxc3x6m or 6.8 to 10.3 xc3xa4ngstrxc3x6m.
Also, with the present invention, it is preferable that the antiferromagnetic layer be formed of a PtMn alloy.
Also, with the present invention, the antiferromagnetic layer may be formed of an Xxe2x80x94Mn alloy (wherein X is one or a plurality of the following elements: Pd, Ir, Rh, Ru, and Os), or formed of a PtMnxe2x80x94Xxe2x80x2 alloy (wherein Xxe2x80x2 is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os, Au, and Ag).
According to the present invention, the spin-valve magnetoresistive thin film element may comprise a single spin-valve magnetoresistive thin film element consisting of one layer each of the antiferromagnetic layer, first pinned magnetic layer, nonmagnetic intermediate layer, second pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer. With this arrangement, it is preferable that the thickness of the antiferromagnetic layer be in a range of 90 to 200 xc3xa4ngstrxc3x6m, and even more preferably in a range of 100 to 200 xc3xa4ngstrxc3x6m.
Or, the spin-valve magnetoresistive thin film element may be a dual spin-valve magnetoresistive thin film element comprising: nonmagnetic electrically conductive layers formed above and below with the free magnetic layer as the center; the three layers of the second pinned magnetic layer/nonmagnetic intermediate layer/first pinned magnetic layer formed above one of the nonmagnetic electrically conductive layer and below the other nonmagnetic electrically conductive layer; and antiferromagnetic layers formed above one of the first pinned magnetic layers and below the other first pinned magnetic layer; and with this arrangement, it is preferable that the thickness of the antiferromagnetic layer be in a range of 100 to 200 xc3xa4ngstrxc3x6m, and even more preferably in a range of 110 to 200 xc3xa4ngstrxc3x6m.
Also, it is preferable that the nonmagnetic intermediate layer introduced between the first free magnetic layer and second free magnetic layer be formed of one of the following, or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu.
It is preferable that the thickness of the nonmagnetic intermediate layer be 5.5 to 10.0 xc3xa4ngstrxc3x6m, and more preferably, 5.9 to 9.4 xc3xa4ngstrxc3x6m.
Further, a thin film magnetic head according to the present invention comprises shield layers formed above and below the spin-valve magnetoresistive thin film element, with gap layers introduced therebetween.
With the present invention, the pinned magnetic layer making up the spin-valve magnetoresistive thin film element is divided into two layers, with a nonmagnetic intermediate layer introduced between the pinned magnetic layers divided into two layers.
The magnetization of the divided two pinned magnetic layers are magnetized so as to be in an antiparallel state, and also are in a so-called Ferri-state wherein the magnitude of the magnetic moment (magnetic film thickness) of one pinned magnetic layer differs from that of the magnetic moment of the other pinned magnetic layer. The exchange coupling magnetic field (RKKY interaction) generated between the two pinned magnetic layers is very large, around 1,000 (Oe) to 5,000 (Oe), so the two pinned magnetic layers are in a very stable state of antiparallel magnetization.
Now, one of the pinned magnetic layers magnetized in the antiparallel state (Ferri-state) is formed so as to be in contact with the antiferromagnetic layer, and the magnetization of the pinned magnetic layer which is in contact with the antiferromagnetic layer (hereafter referred to as the xe2x80x9cfirst pinned magnetic layerxe2x80x9d) is fixed in the direction away from a plane facing a recording medium for example (i.e., the height direction), by the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the pinned magnetic layer and the antiferromagnetic layer. Accordingly, the magnetization of the pinned magnetic layer facing the first pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween (hereafter referred to as the xe2x80x9csecond pinned magnetic layerxe2x80x9d) is pinned in a state antiparallel with the magnetization of the first pinned magnetic layer.
With the present invention, the portion that has been conventionally comprised of the two layers of the antiferromagnetic layer and pinned magnetic layer, is formed of the four layers of antiferromagnetic layer/first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer. Thus, the magnetization state of the first pinned magnetic layer and second pinned magnetic layer can be maintained at an extremely stable state regarding external magnetic fields, but several conditions are necessary in order to further improve the magnetization stability of the first pinned magnetic layer and second pinned magnetic layer.
The first is to increase the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the antiferromagnetic layer and the first pinned magnetic layer. As described above, the magnetization of the first pinned magnetic layer is pinned in a certain direction by the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface with the antiferromagnetic layer, but if this exchange coupling magnetic field is weak, the pinned magnetization of the first pinned magnetic layer does not stabilize, and easily changes due to external magnetic fields and the like. Accordingly, it is preferable that the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface with the antiferromagnetic layer be large. The present invention provides a PtMn alloy as an antiferromagnetic layer whereby a large exchange coupling magnetic field generated at the interface with the first pinned magnetic layer can be obtained. Also, an Xxe2x80x94Mn alloy (wherein X is one or a plurality of the following elements: Pd, Ir, Rh, Ru, and Os), or a PtMnxe2x80x94Xxe2x80x2 alloy (wherein Xxe2x80x2 is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os, Au, and Ag) may be used instead of the PtMn alloy.
These antiferromagnetic materials have excellent properties, as they produce a greater exchange coupling magnetic field than NiO, FeMn alloys, NiMn alloys, and the like which are conventionally used for antiferromagnetic materials, have high blocking temperatures, further have excellent corrosion-resistant properties, and so forth.
FIG. 26 shows R-H curves of a spin-valve magnetoresistive thin film element according to the present invention wherein the pinned magnetic layer is divided into two layers with a nonmagnetic intermediate layer introduced therebetween, using a PtMn alloy for the antiferromagnetic layer, and a known spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is formed as a single layer.
The film configuration of the spin-valve magnetoresistive thin film element according to the present invention is: from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (200)/first pinned magnetic layer of Co (25)/nonmagnetic intermediate layer of Ru (7)/second pinned magnetic layer of Co (20)/Cu (20)/Co (10)/NiFe (40)/Ta (30); wherein the numerals in the parentheses represent film thickness in units of xc3xa4ngstrxc3x6m; whereas the film configuration of the known spin-valve magnetoresistive thin film element is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (300)/pinned magnetic layer of Co (25)/Cu (20)/Co (10)/NiFe (40)/Ta (30).
A spin-valve magnetoresistive thin film element according to the present invention and a known spin-valve magnetoresistive thin film element were both formed, and subjected to thermal treatment at 260xc2x0 C. for four hours while applying a magnetic field of 200 (Oe).
As can be understood from FIG. 26, the xcex94MR (resistance change rate) of the spin-valve magnetoresistive thin film element according to the present invention is between 7 to 8% at the greatest, and the xcex94MR drops by applying a negative external magnetic field, but the xcex94MR in the present invention drops slower than the xcex94MR of the known spin-valve magnetoresistive thin film element.
Now, with the present invention, the magnitude of the external magnetic field at the time that the xcex94MR is half of the maximum value shall be stipulated as the exchange coupling magnetic field (Hex) generated by the spin-valve magnetoresistive thin film element.
As shown in FIG. 26, the maximum xcex94MR of the spin-valve magnetoresistive thin film element according to the present invention is approximately 8%, and the external magnetic field at which the xcex94MR drops to half (the exchange coupling magnetic field (Hex)) is approximately 900 (Oe) absolute value.
In comparison, the maximum xcex94MR of the known spin-valve magnetoresistive thin film element is approximately 7.5%, which is slightly lower than the known arrangement, the external magnetic field at which the xcex94MR drops to half (the exchange coupling magnetic field (Hex)) is approximately 2800 (Oe) absolute value, which is much higher.
Thus, it can be understood that the exchange coupling magnetic field (Hex) can be markedly increased with the spin-valve magnetoresistive thin film element according to the present invention wherein the pinned magnetic layer is divided into two layers, as compared with the known spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is formed of one layer, and the stability of the magnetization of the pinned magnetic layer can be improved in comparison with the known arrangement. Also, the xcex94MR of the present invention does not drop very much as compared with the known arrangement, showing that a high xcex94MR can be maintained.
Next, FIG. 27 is a graph showing the relation between environmental temperature and the exchange coupling magnetic field, using four types of spin-valve magnetoresistive thin film elements.
The first type of spin-valve magnetoresistive thin film element used is a spin-valve magnetoresistive thin film element according to the present invention wherein PtMn is used for the antiferromagnetic layer, and the pinned magnetic layer is divided into two layers. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (200)/first pinned magnetic layer of Co (25)/nonmagnetic intermediate layer of Ru (7)/second pinned magnetic layer of Co (20)/Cu (20)/Co (10)/NiFe (70)/Ta (30).
The second type is a first conventional example wherein a PtMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (300)/pinned magnetic layer of Co (25)/Cu (25)/Co (10)/NiFe (70)/Ta (30).
The third type is a second conventional example wherein NiO is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/antiferromagnetic layer of NiO (500)/pinned magnetic layer of Co (25)/Cu (25)/Co (10)/NiFe (70)/Ta (30).
The fourth type is a third conventional example wherein a FeMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/NiFe (70)/Co (10)/Cu (25)/pinned magnetic layer of Co (25)/antiferromagnetic layer of Femn (150)/Ta (30). In all four types, the numerals in the parentheses represent film thickness in units of xc3xa4ngstrxc3x6m.
The present invention and the first conventional example wherein a PtMn alloy is used for the antiferromagnetic layer are subjected to thermal treatment at 260xc2x0 C. for four hours while applying a magnetic field of 200 (Oe), following formation. The second and third conventional examples wherein NiO and FeMn are used for the antiferromagnetic layer are not subjected to thermal treatment following formation.
As shown in FIG. 27, with the spin-valve magnetoresistive thin film element according to the present invention, the exchange coupling magnetic field (Hex) is approximately 2500 (Oe) under an environment temperature of around 200C, which is very high.
In comparison, with the second conventional example using NiO for the antiferromagnetic layer, and the third conventional example using FeMn for the antiferromagnetic layer, the exchange coupling magnetic field (Hex) is only around 500 (Oe) even under an environment temperature of around 20xc2x0 C., which is low. Also, with the first conventional example using PtMn to form the antiferromagnetic layer, wherein the pinned magnetic layer is formed of a single layer, an exchange coupling magnetic field around 1000 (Oe) is generated under an environment temperature of around 200C, so it can be understood that a greater exchange coupling magnetic field can be obtained than using NiO (second conventional example) or FeMn (third conventional example) for the antiferromagnetic layer.
U.S. Pat. No. 5,701,223 discloses a spin-valve magnetoresistive thin film element which uses NiO for the antiferromagnetic layer, with the pinned magnetic layer being formed of two layers with a nonmagnetic intermediate layer introduced therebetween, and the R-H curve thereof is shown in FIG. 8. According to FIG. 8 of the Patent Publication, an exchange coupling magnetic field (Hex) of 600 (Oe) is then to be obtained, but it can be understood that this is low compared to the exchange coupling magnetic field (around 1000 (Oe), first conventional example) generated wherein a PtMn alloy is used for the antiferromagnetic layer and the pinned magnetic layer is a single layer.
That is to say, if NiO is used for the antiferromagnetic layer, even dividing the pinned magnetic layer into two layers and placing the magnetization of these two layers in a Ferri-state leaves the exchange coupling magnetic field lower than an arrangement wherein a PtMn alloy is used for the antiferromagnetic layer and the pinned magnetic layer is a single layer. Consequently, it can be understood that using the PtMn alloy for the antiferromagnetic layer is preferable from the perspective that a greater exchange coupling magnetic field can be obtained.
Also, as shown in FIG. 27, in the event that NiO or FeMn alloy is used for the antiferromagnetic layer, the exchange coupling magnetic field drops to 0 (Oe) once the environment temperature reaches 200xc2x0 C. This is because the blocking temperature of NiO and FeMn alloys is around 200xc2x0 C., which is low.
Conversely, with the first conventional example wherein the PtMn alloy is used for the antiferromagnetic layer, the exchange coupling magnetic field drops to 0 (Oe) when the environment temperature reaches 400xc2x0 C., so it can be understood that using the PtMn, alloy allows the magnetization state of the pinned magnetic layer in an extremely stable condition, temperature-wise.
The blocking temperature is governed by the material used for the antiferromagnetic layer, so with the spin-valve magnetoresistive thin film element according to the present invention shown in FIG. 27, it can be assumed that the exchange coupling magnetic field drops to 0 (Oe) when the environment temperature reaches 400xc2x0 C., but with arrangements which use PtMn alloys as the antiferromagnetic layer as with the present invention, blocking temperatures higher than using NiO or the like can be obtained, and further, a very large exchange coupling magnetic field can be obtained during the time taken to reach the blocking temperature by means of dividing the pinned magnetic layer into two layers and placing the magnetization of these two layers in a Ferri-state, so the magnetization state of the two pinned magnetic layers can be maintained in an extremely stable condition, temperature-wise.
Also, with the present invention, the nonmagnetic intermediate layer introduced between the first pinned magnetic layer and second pinned magnetic layer is formed of one of the following, or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu. The thickness of the nonmagnetic intermediate layer is changed depending on whether the antiferromagnetic layer is formed above the free magnetic layer or below the free magnetic layer. The nonmagnetic intermediate layer is formed to a thickness within an appropriate range; whereby the exchange coupling magnetic field (Hex) can be increased. The appropriate thickness of the nonmagnetic intermediate layer will be described in detail later, with reference to graphs.
Further, according to the present invention, dividing the pinned magnetic layer into two layers allows a large exchange coupling magnetic field (Hex) to be obtained even if the antiferromagnetic layer formed of PtMn alloy or the like is made thinner, meaning that the antiferromagnetic layer which is the thickest layer in the spin-valve magnetoresistive thin film element configuration can be reduced in thickness, consequently reducing the overall thickness of the spin-valve magnetoresistive thin film element itself. Reducing the thickness of the antiferromagnetic layer allows the distance from the gap layer formed on the underside of the spin-valve magnetoresistive thin film element to the gap layer formed on the upper side of the spin-valve magnetoresistive thin film element, i.e., the gap length, to be reduced, even if the thicknesses of the gap layers formed above and below the spin-valve magnetoresistive thin film element are formed thick enough to maintain sufficient insulation, thereby enabling handling of narrow gapping.
Now, if the pinned magnetic layer is divided into a first pinned magnetic layer and a second pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween, as with the present invention, experimentation has shown that the exchange coupling magnetic field (Hex) and the xcex94MR (rate of resistance change) drops drastically in the event that the first pinned magnetic layer and second pinned magnetic layer are formed at the same thicknesses. It is supposed that this is due to the fact that forming the first pinned magnetic layer and the second pinned magnetic layer at the same thickness makes it difficult to achieve an antiparallel state (Ferri-state) in the magnetization state between the first pinned magnetic layer and the second pinned magnetic layer. Since an antiparallel state cannot be achieved between the first pinned magnetic layer and the second pinned magnetic layer, the relative angle with the fluctuating magnetization of the free magnetic layer cannot be appropriately controlled.
Accordingly, with the present invention, the first pinned magnetic layer and the second pinned magnetic layer are not formed at the same thickness, but rather at differing thicknesses. This allows a large exchange coupling magnetic field to be obtained, and at the same time raises the xcex94MR to around that of known arrangements. The thickness ratio between the first pinned magnetic layer and the second pinned magnetic layer will be described in detail later, with reference to graphs.
As described above, with the present invention, the exchange coupling magnetic field (Hex) of the entire spin-valve magnetoresistive thin film element can be increased by means of dividing the pinned magnetic layer into a first pinned magnetic layer and a second pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween, and by using an antiferromagnetic material such as a PtMn alloy or the like which exhibits a large exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface with the first pinned magnetic layer, as the antiferromagnetic layer. Thus, the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer can be maintained in an extremely stable antiparallel state (Ferri-state), temperature-wise.
With the present invention, the exchange coupling magnetic field of the entire spin-valve magnetoresistive thin film element can be increased and high xcex94MR can be obtained, by optimizing the film thickness ratio between the divided first pinned magnetic layer and second pinned magnetic layer, the material and thickness of the nonmagnetic intermediate layer, the thickness of the antiferromagnetic layer, etc.
Spin-valve magnetoresistive thin film elements to which the present invention may be applied include both so-called single spin-valve magnetoresistive thin film elements consisting of one layer each of the antiferromagnetic layer, pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer, and so-called dual spin-valve magnetoresistive thin film elements comprising nonmagnetic electrically conductive layers, pinned magnetic layers, and antiferromagnetic layers formed above and below with the free magnetic layer as the center.
Further, with the present invention, the free magnetic layer may be divided into two with the nonmagnetic intermediate layer introduced therebetween, as with the pinned magnetic layer. The magnetization of the first free magnetic layer and second free-magnetic layer formed with the nonmagnetic intermediate layer introduced therebetween is magnetized in an antiparallel manner by the exchange coupling magnetic field (RKKY interaction) generated between the first free magnetic layer and second free magnetic layer, and further aligned in a direction intersecting the magnetization of the pinned magnetic layer (first pinned magnetic layer and second pinned magnetic layer).
With the case of the pinned magnetic layer (first pinned magnetic layer and second pinned magnetic layer), the magnetization is pinned in a certain direction by exchange coupling magnetic field (exchange anisotropic magnetic field) with the antiferromagnetic layer. However, the magnetization of the free magnetic layer is made to freely change according to external magnetic fields, so electric resistance changes due to the relationship between change in magnetization of the free magnetic layer and the direction of the pinned magnetization of the pinned magnetic layer, thereby enabling detection of external magnetic field signals.
With the present invention, the antiparallel state (Ferri-state) of the first pinned magnetic layer and the second pinned magnetic layer can be maintained in an extremely stable state temperature-wise, and a high xcex94MR as with known arrangements can be obtained, by optimizing the ratio of the thickness of the first free magnetic layer and second free magnetic layer divided with the nonmagnetic intermediate layer introduced therebetween, and the thickness of the nonmagnetic intermediate layer. The ratio of the thickness of the first free magnetic layer and second free magnetic layer and the thickness of the nonmagnetic intermediate layer will be described later in detail with reference to graphs.
Also, a second aspect of the present invention provides a spin-valve magnetoresistive thin film element, comprising: an antiferromagnetic layer; a pinned magnetic layer formed in a manner contacting the antiferromagnetic layer. The magnetizing direction is pinned by the exchange coupling magnetic field between the pinned magnetic layer and the antiferromagnetic layer. A nonmagnetic electrically conductive layer formed between a free magnetic layer and the pinned magnetic layer, wherein the magnetizing direction of the free magnetic layer is aligned so as to intersect with the magnetizing direction of the pinned magnetic layer. Electric resistance, which changes according to the relationship between pinned magnetization of the pinned magnetic layer and fluctuating magnetization of the free magnetic layer, is detected by means of a sensing current being caused to flow in a direction intersecting the pinned magnetization of the pinned magnetic layer.
The pinned magnetic layer is divided into the two layers of a first pinned magnetic layer which comes in contact with the antiferromagnetic layer and a second pinned magnetic layer which comes in contact with the nonmagnetic electrically conductive layer, with a nonmagnetic intermediate layer introduced therebetween.
The sensing current is caused to flow in a direction such that the direction of the sensing current magnetic field formed at the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion by means of causing the sensing current to flow, and the direction of a synthesized magnetic moment formed by adding the magnetic moment of the first pinned magnetic layer (wherein saturation magnetization is Ms and film thickness is t) and the magnetic moment of the second pinned magnetic layer, are the same direction.
Also, with the present invention, the spin-valve magnetoresistive thin film element may be a single spin-valve magnetoresistive thin film element consisting of one layer each of the antiferromagnetic layer, first pinned magnetic layer, nonmagnetic intermediate layer, second pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer.
If the magnetic moment of the first pinned magnetic layer is greater than the magnetic moment of the second pinned magnetic layer, the sensing current must be caused to flow in a direction such that the direction of the sensing current magnetic field formed at the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion by means of causing the sensing current to flow, and the direction of the magnetic moment of the first pinned magnetic layer, are the same direction or, the spin-valve magnetoresistive thin film element may be a single spin-valve magnetoresistive thin film element consisting of one layer each of the antiferromagnetic layer, first pinned magnetic layer, nonmagnetic intermediate layer, second pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer.
If the magnetic moment of the first pinned magnetic layer is smaller than the magnetic moment of the second pinned magnetic layer, the sensing current must be caused to flow in a direction such that the direction of the sensing current magnetic field formed at the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion by means of causing the sensing current to flow, and the direction of the magnetic moment of the second pinned magnetic layer, are the same direction.
Also, with the present invention, the free magnetic layer preferably is divided into two layers with a nonmagnetic intermediate layer introduced therebetween. Further, the nonmagnetic intermediate layer introduced between the free magnetic layer divided into two layers is preferably formed of one of the following; or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu.
Also, according to the present invention, the spin-valve magnetoresistive thin film element may be a dual spin-valve magnetoresistive thin film element comprising: nonmagnetic electrically conductive layers formed above and below with the free magnetic layer as the center. The three layers of the second pinned magnetic layer/nonmagnetic intermediate layer/first pinned magnetic layer are formed above one of the nonmagnetic electrically conductive layer and below the other nonmagnetic electrically conductive layer. The antiferromagnetic layers are formed above one of the first pinned magnetic layers and below the other first pinned magnetic layer. The synthesized magnetic moment of the first pinned magnetic layer and the second pinned magnetic layer formed to the upper side of the free magnetic layer, and the synthesized magnetic moment of the first pinned magnetic layer and the second pinned magnetic layer formed to the lower side of the free magnetic layer, are facing in mutually opposite directions.
The sensing current must be caused to flow in a direction such that the direction of the sensing current magnetic field formed at the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion by causing the sensing current to flow, and the direction of the synthesized magnetic moment formed above and below the free magnetic layer, are the same direction.
With regard to specific magnitude of the magnetic moment of the first pinned magnetic layer and second pinned magnetic layer in the above-described dual spin-valve magnetoresistive thin film element, it is necessary that the magnetic moment of the first pinned magnetic layer formed to the upper side of the free magnetic layer be greater than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer; and that the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer be smaller than the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer; and further that the pinned magnetization of the first pinned magnetic layers formed above and below the free magnetic layer be facing in the same direction.
Or, it is necessary that the magnetic moment of the first pinned magnetic layer formed to the upper side of the free magnetic layer be smaller than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer; and that the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer be greater than the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer; and further that the pinned magnetization of the first pinned magnetic layers formed above and below the free magnetic layer be facing in the same direction.
With the present invention, it is preferable that the antiferromagnetic layer be formed of a PtMn alloy.
Or, the antiferromagnetic layer may be formed of an Xxe2x80x94Mn alloy (wherein X is one or a plurality of the following elements: Pd, Ir, Rh, Ru,Os), or a PtMnxe2x80x94Xxe2x80x2 alloy (wherein Xxe2x80x2 is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os, Au, Ag).
Also, with the present invention, it is preferable that the nonmagnetic intermediate layer introduced between the first pinned magnetic layer and second pinned magnetic layer be formed of one of the following; or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu.
Also, a thin film magnetic head according to the present invention comprises shield layers formed above and below the above-described spin-valve magnetoresistive thin film element, with gap layers introduced therebetween.
With the present invention, the pinned magnetic layer making up the spin-valve magnetoresistive thin film element is divided into two layers, with a nonmagnetic intermediate layer introduced between the pinned magnetic layers divided into two layers.
The magnetization of the divided two pinned magnetic layers are magnetized so as to be in an antiparallel state, and also are in a so-called Ferri-state wherein the magnitude of the magnetic moment of one pinned magnetic layer differs from the magnetic moment of the other pinned magnetic layer. The exchange coupling magnetic field (RKKY interaction) generated between the two pinned magnetic layers is very large, around 1,000 (Oe) to 5,000 (Oe), so the two pinned magnetic layers are in a very stable state of antiparallel magnetization.
Now, one of the pinned magnetic layers magnetized in the antiparallel state (Ferri-state) is formed so as to be in contact with the antiferromagnetic layer, and the magnetization of the pinned magnetic layer which is in contact with the antiferromagnetic layer (hereafter referred to as the xe2x80x9cfirst pinned magnetic layerxe2x80x9d) is fixed in the direction away from a plane facing a recording medium for example (i.e., the height direction), by the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the pinned magnetic layer and the antiferromagnetic layer. Accordingly, the magnetization of the pinned magnetic layer facing the first pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween (hereafter referred to as the xe2x80x9csecond pinned magnetic layerxe2x80x9d) is pinned in a state antiparallel with the magnetization of the first pinned magnetic layer.
With the present invention, the portion that has been conventionally comprised of the two layers of the antiferromagnetic layer and pinned magnetic layer, is formed of the four layers of antiferromagnetic layer/first pinned magnetic layer/nonmagnetic intermediate layer/second. pinned magnetic layer, whereby the magnetization state of the first pinned magnetic layer and second pinned magnetic layer can be maintained at an extremely stable state regarding external magnetic fields.
Now, in recent years, recording density has increased, and accordingly, increase in temperature within the device owing to increase of the revolutions of the recording medium, increase in temperature due to increase of sensing current, and increase of sensing current magnetic fields may make the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer unstable.
The sensing current is caused to flow in a direction intersecting with the magnetization direction of the first pinned magnetic layer and the second pinned magnetic layer (i.e., in the same direction as the magnetization direction in the free magnetic layer, or the opposite direction), but a sensing current magnetic field is formed by the corkscrew rule by causing the sensing current to flow, and this sensing current magnetic field intrudes into the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion, in the same or opposite magnetization direction as the first pinned magnetic layer (or second pinned magnetic layer).
As described above, the magnetic moment of the first pinned magnetic layer is formed so as to differ from the magnetic moment of the second pinned magnetic layer, thereby placing the magnetization of the first pinned magnetic layer and the second pinned magnetic layer in an antiparallel magnetized state. With the present invention, the difference in magnitude of the magnetic moment of the first pinned magnetic layer and the second pinned magnetic layer is used to cause the sensing current to flow in an appropriate direction, so that the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer is placed in a thermally more stable state, by the sensing current magnetic field.
Specifically, with the spin-valve magnetoresistive thin film element, if the magnetic moment of the first pinned magnetic layer is greater than the magnetic moment of the second pinned magnetic layer, the synthesized magnetic moment which can be obtained by adding the magnetic moment of the first pinned magnetic layer and the magnetic moment of the second pinned magnetic layer faces the same direction as the magnetic moment of the first pinned magnetic layer.
Then, the present invention allows the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer to be in a thermally more stable state, by adjusting the direction of causing the sensing current to flow, so that the sensing current magnetic field formed at the portion of the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion and the direction of the synthesized magnetic moment match.
Further, with the present invention, a dual spin-valve magnetoresistive thin film element allows the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer to be in a thermally stable state, by adjusting the magnetic moment and so forth of the first pinned magnetic layer and the magnetic moment of the second pinned magnetic layer such that the synthesized magnetic moments formed above and below the free magnetic layer are mutually opposing, thereby causing the sensing current to flow such that the sensing current magnetic field formed at the portion of the first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer portion and the direction of the synthesized magnetic moment match.
Also, according to the present invention, several conditions other than the direction of the sensing current are used in order to improve the magnetization stability of the first pinned magnetic layer and second pinned magnetic layer.
The first is to increase the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the antiferromagnetic layer and the first pinned magnetic layer. As described above, the magnetization of the first pinned magnetic layer is pinned in a certain direction by the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface with the antiferromagnetic layer, but if this exchange coupling magnetic field is weak, the pinned magnetization of the first pinned magnetic layer does not stabilize, and easily changes due to external magnetic fields and the like. Accordingly, it is preferable that the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface with the antiferromagnetic layer be great, and the present invention gives a PtMn alloy as an antiferromagnetic layer whereby a large exchange coupling magnetic field generated at the interface with the first pinned magnetic layer can be obtained. Also, an Xxe2x80x94Mn alloy (wherein X is one or a plurality of the following elements: Pd, Ir, Rh, Ru, and Os), or a PtMnxe2x80x94Xxe2x80x2 alloy (wherein Xxe2x80x2 is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os, Au, and Ag) may be used instead of the PtMn alloy.
These antiferromagnetic materials have excellent properties, as they produce a greater exchange coupling magnetic field than NiO, FeMn alloys, NiMn alloys, and the like conventionally used for antiferromagnetic materials, have high blocking temperatures, further have excellent corrosion-resistant properties, and so forth.
FIG. 26 shows R-H curves of the spin-valve magnetoresistive thin film element according to the present invention using a PtMn alloy for the antiferromagnetic layer, wherein the pinned magnetic layer is divided into two layers with a nonmagnetic intermediate layer introduced therebetween, and a known spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is formed as a single layer.
The film configuration of the spin-valve magnetoresistive thin film element according to the present invention is: from the bottom; the Si substrate/Alumina/Ta (30)/antiferromagnetic layer of PtMn (200)/first pinned magnetic layer of Co (25)/nonmagnetic intermediate layer of Ru (7)/second pinned magnetic layer of Co (20)/Cu (20)/Co (10)/NiFe (40)/Ta (30); wherein the numerals in the parentheses represent film thickness in units of xc3x85ngstrxc3x6m; whereas the film configuration of the known spin-valve magnetoresistive thin film element is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (300)/pinned magnetic layer of Co (25)/Cu (20)/Co (10)/NiFe (40)/Ta (30).
A spin-valve magnetoresistive thin film element according to the present invention and a known spin-valve magnetoresistive thin film element were both formed, and subjected to thermal treatment at 260xc2x0 C. for four hours while applying a magnetic field of 200 (Oe).
As can be understood from FIG. 26, the xcex94MR (resistance change rate) of the spin-valve magnetoresistive thin film element according to the present invention is between 7 to 8% at the greatest, and the xcex94MR drops by applying a negative external magnetic field, but the xcex94MR in the present invention drops slower than the xcex94MR of the known spin-valve magnetoresistive thin film element.
Now, with the present invention, the magnitude of the external magnetic field at the time that the xcex94MR is half of the maximum value shall be stipulated as the exchange coupling magnetic field (Hex) generated by the spin-valve magnetoresistive thin film element.
As shown in FIG. 26, the maximum xcex94MR of the known spin valve magnetoresistive thin film element is approximately 8%, and the external magnetic field at which the xcex94MR drops to half (the exchange coupling magnetic field (Hex)) is approximately 900 (Oe) absolute value.
In comparison, with the present invention the maximum xcex94MR of the known spin-valve magnetoresistive thin film element is approximately 7.5%, which is slightly lower than the known arrangement, the external magnetic field at which the xcex94MR drops to half (the exchange coupling magnetic field (Hex)) is approximately 2800 (Oe) absolute value, which is much higher.
Thus, it can be understood that the exchange coupling magnetic field (Hex) can be markedly increased with the spin-valve magnetoresistive thin film element according to the present invention wherein the pinned magnetic layer is divided into two layers, as compared with the known spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is formed of one layer, and the stability of the magnetization of the pinned magnetic layer can be improved in comparison with the known arrangement. Also, the xcex94MR of the present invention does not drop very much as compared with the known arrangement, showing that a high xcex94MR can be maintained.
Next, FIG. 27 is a graph showing the relation between environmental temperature and the exchange coupling magnetic field, using four types of spin-valve magnetoresistive thin film elements.
The first type of spin-valve magnetoresistive thin film element used is a spin-valve magnetoresistive thin film element according to the present invention wherein a PtMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is divided into two layers. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (200)/first pinned magnetic layer of Co (25)/nonmagnetic intermediate layer of Ru (7)/second pinned magnetic layer of Co (20)/Cu (20)/Co (10)/NiFe (70)/Ta (30).
The second type is a first conventional example wherein a PtMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (300)/pinned magnetic layer of Co (25)/Cu (25)/Co (10)/NiFe (70)/Ta (30).
The third type is a second conventional example wherein NiO is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2 O3/antiferromagnetic layer of NiO (500)/pinned magnetic layer of Co (25)/Cu (25)/Co (10)/NiFe (70)/Ta (30).
The fourth type is a third conventional example wherein an FeMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/NiFe (70)/Co (10)/Cu (25)/pinned magnetic layer of Co (25)/antiferromagnetic layer of FeMn (150)/Ta (30). In all four types, the numerals in the parentheses represent film thickness in units of xc3xa4ngstrxc3x6m.
The present invention and the first conventional example wherein a PtMn alloy is used for the antiferromagnetic layer are subjected to thermal treatment at 260xc2x0 C. for four hours while applying a magnetic field of 200 (Oe), following formation. The second and third conventional examples wherein NiO and FeMn are used for the antiferromagnetic layer are not subjected to thermal treatment following formation.
As shown in FIG. 27, with the spin-valve magnetoresistive thin film element according to the present invention, the exchange coupling magnetic field (Hex) is approximately 2,500 (Oe) under an environment temperature of around 200xc2x0 C., which is very high.
In comparison, with the second conventional example using NiO for the antiferromagnetic layer, and the third conventional example using FeMn for the antiferromagnetic layer, the exchange coupling magnetic field (Hex) is only around 500 (Oe) even under an environment temperature of around 20xc2x0 C., which is low. Also, with the first conventional example using PtMn to form the antiferromagnetic layer, wherein the pinned magnetic layer is formed of a single layer, an exchange coupling magnetic field (Hex) around 1,000 (Oe) is generated under an environment temperature of around 200xc2x0 C., so it can be understood that a greater exchange coupling magnetic field can be obtained than using NiO (second conventional example) or FeMn (third conventional example) for the antiferromagnetic layer.
U.S. Pat. No. 5,701,223 discloses a spin-valve magnetoresistive thin film element which uses NiO for the antiferromagnetic layer, with the pinned magnetic layer being formed of two layers with a nonmagnetic intermediate layer introduced therebetween, and the R-H curve thereof is shown in FIG. 8. According to FIG. 8 of the Patent Publication, an exchange coupling magnetic field (Hex) of 600 (Oe) is then to be obtained, but it can be understood that this is low compared to the exchange coupling magnetic field (around 1000 (Oe), first conventional example) generated wherein a PtMn alloy is used for the antiferromagnetic layer and the pinned magnetic layer is a single layer.
That is to say, in the event that NiO is used for the antiferromagnetic layer, even dividing the pinned magnetic layer into two layers and placing the magnetization of these two layers in a Ferri-state leaves the exchange coupling magnetic field lower than an arrangement wherein a PtMn alloy is used for the antiferromagnetic layer and the pinned magnetic layer is a single layer. Consequently, it can be understood that using the PtMn alloy for the antiferromagnetic layer is preferable from the perspective that a greater exchange coupling magnetic field can be obtained.
Also, as shown in FIG. 27, if NiO or FeMn alloy is used for the antiferromagnetic layer, the exchange coupling magnetic field drops to 0 (Oe) once the environment temperature reaches 200xc2x0 C. This is because the blocking temperature of NiO and FeMn alloys is around 200xc2x0 C., which is low.
Conversely, with the first conventional example wherein the PtMn alloy is used for the antiferromagnetic layer, the exchange coupling magnetic field drops to 0 (Oe) when the environment temperature reaches 400xc2x0 C., so it can be understood that using the PtMn alloy allows the magnetization state of the pinned magnetic layer in an extremely stable condition, temperature-wise.
The blocking temperature is governed by the material used for the antiferromagnetic layer, so with the spin-valve magnetoresistive thin film element according to the present invention shown in FIG. 27, it can be assumed that the exchange coupling magnetic field drops to 0 (Oe) when the environment temperature reaches 400xc2x0 C., but with arrangements which use PtMn alloys as the antiferromagnetic material as with the present invention, blocking temperatures higher than using NiO or the like can be obtained, and further, a very large exchange coupling magnetic field can be obtained during the time taken to reach the blocking temperature by dividing the pinned magnetic layer into two layers and placing the magnetization of these two layers in a Ferri-state, so the magnetization state of the two pinned magnetic layers can be maintained in a thermally stable condition.
Also, with the present invention, the nonmagnetic intermediate layer introduced between the first pinned magnetic layer and second pinned magnetic layer is formed of one of the following, or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu; the thickness of the nonmagnetic intermediate layer is changed depending on whether the antiferromagnetic layer is formed above the free magnetic layer or below the free magnetic layer; and the nonmagnetic intermediate layer is formed to a thickness within an appropriate range; whereby the exchange coupling magnetic field (Hex) can be increased. The appropriate thickness of the nonmagnetic intermediate layer will be described in detail later, with reference to graphs.
Further, according to the present invention, dividing the pinned magnetic layer into two layers allows a large exchange coupling magnetic field (Hex) to be obtained even if the antiferromagnetic layer formed of PtMn alloy or the like is made thinner, meaning that the antiferromagnetic layer which is the thickest layer in the spin-valve magnetoresistive thin film element configuration can be reduced in thickness, consequently reducing the overall thickness of the spin-valve magnetoresistive thin film element itself. Reducing the thickness of the antiferromagnetic layer allows the distance from the gap layer formed on the underside of the spin-valve magnetoresistive thin film element to the gap layer formed on the upper side of the spin-valve magnetoresistive thin film element, i.e., the gap length, to be reduced, even if the thicknesses of the gap layers formed above and below the spin-valve magnetoresistive thin film element are formed thick enough to maintain sufficient insulation, thereby enabling handling of narrow gapping.
Now, in the event that the pinned magnetic layer is divided into a first pinned magnetic layer and a second pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween, as with the present invention, experimentation has shown that the exchange coupling magnetic field (Hex) and the xcex94MR (rate of resistance change) drops drastically in the event that the first pinned magnetic layer and second pinned magnetic layer are formed at the same thicknesses. It is supposed that this is due to the fact that forming the first pinned magnetic layer and the second pinned magnetic layer at the same thickness makes it difficult to achieve an antiparallel state (Ferri-state) in the magnetization state between the first pinned magnetic layer and the second pinned magnetic layer. Since an antiparallel state cannot be achieved between the first pinned magnetic layer and the second pinned magnetic layer, the relative angle with the fluctuating magnetization of the free magnetic layer cannot be appropriately controlled.
Accordingly, with the present invention, the first pinned magnetic layer and the second pinned magnetic layer are not formed at the same thickness, but rather at differing thicknesses, thereby allowing a large exchange coupling magnetic field to be obtained, and at the same time raising the xcex94MR to around that of known arrangements. The thickness ratio between the first pinned magnetic layer and the second pinned magnetic layer will be described in detail later, with reference to graphs.
As described above, with the present invention, the exchange coupling magnetic field (Hex) of the entire spin-valve magnetoresistive thin film element can be increased by dividing the pinned magnetic layer into a first pinned magnetic layer and a second pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween, and by using an antiferromagnetic material such as a PtMn alloy or the like which exhibits a large exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface with the first pinned magnetic layer, as the antiferromagnetic layer, so the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer can be maintained in a stable antiparallel state (Ferri-state), temperature-wise.
Particularly, with the present invention, the direction of the sensing current magnetic field formed by the flow of sensing current and the direction of the synthesized magnetic moment which can be obtained by adding the magnetic moment of the first pinned magnetic layer and the magnetic moment of the second pinned magnetic layer are made to match by controlling the direction in which the sensing current is made to flow, so the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer can be maintained in an even more thermally stable state.
A third aspect of the present invention is a method for manufacturing a single spin-valve magnetoresistive thin film element, wherein the thin film element comprises: an antiferromagnetic layer; a pinned magnetic layer formed in a manner contacting the antiferromagnetic layer, wherein the magnetization thereof is pinned in a certain direction by the exchange coupling magnetic field generated at the interface between the pinned magnetic layer and the antiferromagnetic layer by thermal treatment in a magnetic field; and a magnetic electrically conductive layer formed between a free magnetic layer and the pinned magnetic layer, wherein the magnetizing direction of the free magnetic layer is aligned so as to intersect with the magnetizing direction of the pinned magnetic layer; and wherein the thin film element consists of one layer each of an antiferromagnetic layer, pinned magnetic layer, nonmagnetic electrically conductive layer, and free magnetic layer.
The method comprises the steps of:
a process for forming the magnetic moment of the first pinned magnetic layer (wherein saturation magnetization is Ms and film thickness is t) and the magnetic moment of the second pinned magnetic layer so as to differ in size, at the time that the pinned magnetic layer is divided into the two layers of a first pinned magnetic layer coming into contact with the antiferromagnetic layer and a second pinned magnetic layer coming into contact with the nonmagnetic electrically conductive layer, with a nonmagnetic intermediate layer introduced therebetween; and
a process wherein, at the time of conducting thermal treatment in a magnetic field following forming the single spin-valve magnetoresistive thin film element, a magnetic field of 100 to 1,000 Oe or a magnetic field of 5 kOe or greater is applied in the direction in which pointing of the magnetization of the first pinned magnetic layer is desired if the magnetic moment of the first pinned magnetic layer is. greater than the magnetic moment of the second pinned magnetic layer, or, a magnetic field of 100 to 1,000 Oe is applied in the direction opposite to which pointing of the magnetization of the first pinned magnetic layer is desired or a magnetic field of 5 kOe or greater is applied in the direction in which pointing of the magnetization of the first pinned magnetic layer is desired if the magnetic moment of the first pinned magnetic layer is smaller than the magnetic moment of the second pinned magnetic layer. With the present invention, the layers for the single spin-valve magnetoresistive thin film element may be formed from the bottom in the order of: the antiferromagnetic layer, the first pinned magnetic layer, the nonmagnetic intermediate layer, the second pinned magnetic layer, the nonmagnetic electrically conductive layer, and the free magnetic layer, or may be formed from the bottom in the order of: the free magnetic layer, the nonmagnetic electrically conductive layer, the second pinned magnetic layer, the nonmagnetic intermediate layer, the first pinned magnetic layer, and the antiferromagnetic layer.
Also, with the present invention, the free magnetic layer may be divided into two layers with a nonmagnetic intermediate layer introduced therebetween.
Also, the present invention provides a method for manufacturing a dual spin-valve magnetoresistive thin film element, this spin-valve magnetoresistive thin film element comprising: nonmagnetic electrically conductive layers formed above and below the free magnetic layer with the free magnetic layer as the center; pinned magnetic layers formed above one of the nonmagnetic electrically conductive layers and below the other nonmagnetic electrically conductive layer, having the magnetization thereof pinned in one direction; and antiferromagnetic layers formed above one of the pinned magnetic layer and below the other pinned magnetic layer.
The method comprises the steps of:
a process for creating difference in divided pinned magnetic layers formed above and below the free magnetic layer at the time of dividing the pinned magnetic layer into the two layers of a first pinned magnetic layer coming into contact with the antiferromagnetic layer and a second pinned magnetic layer coming into contact with the nonmagnetic electrically conductive layer, with the nonmagnetic intermediate layer introduced therebetween, such that the magnetic moment of the first pinned magnetic layer (wherein saturation magnetization is Ms and film thickness is t) formed to the upper side of the free magnetic layer is greater than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer, and also so that the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer is smaller than the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer, or, such that the magnetic moment of the first pinned magnetic layer formed to the upper side of the free magnetic layer is smaller than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer, and also so that the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer is greater than the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer; and
a process for applying a magnetic field of 5 kOe or greater in the direction in which pointing of the magnetization of the first pinned magnetic layer is desired, at the time of generating the exchange coupling magnetic field generated at the interface between the first pinned magnetic layer and the antiferromagnetic layer formed above and below the free magnetic layer, by thermal treatment in a magnetic field following formation of the films of the dual spin-valve magnetoresistive thin film element, thereby pinning the magnetization of both first pinned magnetic layers in the same direction.
Also, the present invention may be arranged such that the magnetic moment of the first pinned magnetic layer formed to the upper side of the free magnetic layer is made to be greater than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer, and also the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer is made to be greater than the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer, and a magnetic field of 100 to 1,000 Oe or a magnetic field of 5 kOe or greater is applied in the direction in which pointing of the magnetization of the first pinned magnetic layer is desired, or, such that the magnetic moment of the first pinned magnetic layer formed to the upper side of the free magnetic layer is made to be smaller than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer, and also the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer is made to be smaller than the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer, and a magnetic field of 100 to 1,000 Oe is applied in the direction opposite to which pointing of the magnetization of the first pinned magnetic layer is desired, or a magnetic field of 5 kOe or greater is applied in the direction in which pointing of the magnetization of the first pinned magnetic layer is desired, thereby pinning the magnetization of both first pinned magnetic layers formed above and below the free magnetic layer in the same direction.
Further, the present invention provides another method for manufacturing a dual spin-valve magnetoresistive thin film element, this spin-valve magnetoresistive thin film element comprising: nonmagnetic electrically conductive layers formed above and below the free magnetic layer with the free magnetic layer as the center; pinned magnetic layers formed above one of the nonmagnetic electrically conductive layers and below the other nonmagnetic electrically conductive layer, having the magnetization thereof pinned in one direction; and antiferromagnetic layers formed above one of the pinned magnetic layer and below the other pinned magnetic layer.
The method comprises the steps of:
a process for dividing the free magnetic layer into the two layers of a first free magnetic layer and a second free magnetic layer with a nonmagnetic intermediate layer introduced therebetween, and aligning the magnetization of the first pinned magnetic layer and the magnetization of the second pinned magnetic layer in an antiparallel manner;
a process for creating difference in divided pinned magnetic layers at the time of dividing the pinned magnetic layer into the two layers of a first pinned magnetic layer and a second pinned magnetic layer, with the nonmagnetic intermediate layer introduced therebetween, such that the magnetic moment of the first pinned magnetic layer (wherein saturation magnetization is Ms and film thickness is t) formed to the upper side of the free magnetic layer is greater than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer, and also so that the magnetic moment of the first pinned magnetic layer (wherein saturation magnetization is Ms and film thickness is t) formed to the lower side of the free magnetic layer is smaller than the magnetic moment of the second pinned magnetic layer (wherein saturation magnetization is Ms and film thickness is t) formed to the lower side of the free magnetic layer, or, such that the magnetic moment of the first pinned magnetic layer formed to the upper side of the free magnetic layer is smaller than the magnetic moment of the second pinned magnetic layer formed to the upper side of the free magnetic layer, and al so so that the magnetic moment of the first pinned magnetic layer formed to the lower side of the free magnetic layer is greater th a n the magnetic moment of the second pinned magnetic layer formed to the lower side of the free magnetic layer; and
a process for applying a magnetic field of 100 to 1,000 Oe in the direction in which pointing of the magnetization of the first pinned magnetic layer is desired, at the time of generating an exchange coupling magnetic field at the interface between the first pinned magnetic layer and the antiferromagnetic layer formed above and below the free magnetic layer, by thermal treatment in a magnetic field following forming the dual spin-valve magnetoresistive thin film element, thereby aligning and pinning the magnetization of the first pinned magnetic layers formed above and below the free magnetic layer in an antiparallel manner.
Also, with the present invention, the antiferromagnetic layer is preferably formed of a PtMn alloy. Further, the antiferromagnetic layer may be formed of an Xxe2x80x94Mn alloy (wherein X is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os), or a PtMnxe2x80x94Xxe2x80x2 alloy (wherein Xxe2x80x2, is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os, Au, Ag), instead of the PtMn alloy.
Further, according to the present invention, the nonmagnetic intermediate layer introduced between the first pinned magnetic layer and second pinned magnetic layer, and the nonmagnetic intermediate layer introduced between the first free magnetic layer and second free magnetic layer, are preferably formed of one of the following; or of an alloy of two or more thereof: Ru, Rh, Ir, Cr, Re, and Cu.
Also, the present invention is a method for manufacturing a thin film magnetic head, the head comprising: the above-described spin-valve magnetoresistive thin film element formed above a lower shield layer with a gap layer introduced therebetween; and an upper shield layer formed above the spin-valve magnetoresistive thin film element, with a gap layer introduced therebetween.
With the present invention, the pinned magnetic layer making up the spin-valve magnetoresistive thin film element is divided into two layers, with a nonmagnetic intermediate layer introduced between the pinned magnetic layers divided into two layers.
The magnetization of the two divided pinned magnetic layers are magnetized so as to be in an antiparallel state, and also are in a so-called Ferri-state wherein the magnitude of the magnetic moment of one pinned magnetic layer differs from the magnetic moment of the other pinned magnetic layer. The exchange coupling magnetic field (RKKY interaction) generated between the two pinned magnetic layers is very large, around 1,000 (Oe) to 5,000 (Oe), so the two pinned magnetic layers are in a very stable state of antiparallel magnetization.
Now, one of the pinned magnetic layers magnetized in the antiparallel state (Ferri-state) is formed so as to be in contact with the antiferromagnetic layer, and the magnetization of the pinned magnetic layer which is in contact with the antiferromagnetic layer (hereafter referred to as the xe2x80x9cfirst pinned magnetic layerxe2x80x9d) is pinned in the direction away from a plane facing a recording medium for example (i.e., the height direction), by the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the pinned magnetic layer and the antiferromagnetic layer. Accordingly, the magnetization of the pinned magnetic layer facing the first pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween (hereafter referred to as the xe2x80x9csecond pinned magnetic layerxe2x80x9d) is pinned in a state antiparallel with the magnetization of the first pinned magnetic layer.
With the present invention, the portion that has been conventionally comprised of the two layers of the antiferromagnetic layer and pinned magnetic layer, is formed of the four layers of antiferromagnetic layer/first pinned magnetic layer/nonmagnetic intermediate layer/second pinned magnetic layer, whereby the magnetization state of the first pinned magnetic layer and second pinned magnetic layer can be maintained at an extremely stable state regarding external magnetic fields. Particularly, in cases such as with the present invention wherein antiferromagnetic material is used for generating an exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface between the first pinned magnetic layer and the antiferromagnetic layer by performing thermal treatment in a magnetic field, the direction and magnitude of the magnetic field during thermal treatment must be controlled appropriately, or the magnetization of the first pinned magnetic layer and second pinned magnetic layer cannot be maintained in an antiparallel state.
Also, a problem that arises regarding the magnetization control of the first pinned magnetic layer and second pinned magnetic layer is the relationship between the fluctuating magnetization of the free magnetic layer and the pinned magnetization of the second pinned magnetic layer formed above and below the free magnetic layer, in the case of dual spin-valve magnetoresistive thin film elements.
With dual spin-valve magnetoresistive thin film elements, nonmagnetic electrically conductive layers and pinned magnetic layers are formed above and below the free magnetic layer, so a greater xcex94MR (the rate of resistance change) can be expected as compared to single spin-valve magnetoresistive thin film elements. However, the rate of resistance change according to the relationship between the fluctuating magnetization of the free magnetic layer, and the second pinned magnetic layer formed above the free magnetic layer with a nonmagnetic electrically conductive layer introduced therebetween; and the rate of resistance change according to the relationship between the fluctuating magnetization of the free magnetic layer, and the second pinned magnetic layer formed below the free magnetic layer with a nonmagnetic electrically conductive layer introduced therebetween; must both exhibit the same fluctuation, and the direction of pinned magnetization of the second pinned magnetic layer must be appropriately controlled to this end.
That is, the direction of pinned magnetization of the second pinned magnetic layer must be appropriately controlled so that in the event that the rate of resistance change at the upper side of the free magnetic layer is maximum, the rate of resistance change at the lower side of the free magnetic layer must also be made to be maximum, and in the event that the rate of resistance change at the upper side of the free magnetic layer is minimum, the rate of resistance change at the lower side of the free magnetic layer must also be made to be minimum.
Accordingly, with the present invention, the magnitude of the values of magnetic moment at the first pinned magnetic layer and magnetic moment at the second pinned magnetic layer are appropriately adjusted, along with adjusting the size and direction of the magnetic field applied during thermal treatment, thereby appropriately controlling the pinned magnetization direction of the first pinned magnetic layer and the pinned magnetization direction of the second pinned magnetic layer.
Next, with reference to FIG. 21, the difference between a spin-valve magnetoresistive thin film element according to the present invention wherein the pinned magnetic layer is divided into a first pinned magnetic layer and second pinned magnetic layer, and a known hysteresis loop wherein the pinned magnetic layer is formed of a single layer, will be described.
FIG. 26 shows R-H curves of the spin-valve magnetoresistive thin film element according to the present invention, wherein a PtMn alloy is used as the antiferromagnetic layer and the pinned magnetic layer is divided into the two layers of the first pinned magnetic layer and second pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween, and a known spin-valve magnetoresistive thin film element, wherein the pinned magnetic layer is formed as a single layer.
The film configuration of the spin-valve magnetoresistive thin film element according to the present invention is: from the bottom; the Si substrate/Alumina/Ta (30)/antiferromagnetic layer of PtMn (200)/first pinned magnetic layer of Co (25)/nonmagnetic intermediate layer of Ru (7)/second pinned magnetic layer of Co (20)/Cu (20)/Co (10)/NiFe (40)/Ta (30); wherein the numerals in the parentheses represent film thickness in units of xc3xa4ngstrxc3x6m whereas the film configuration of the known spin-valve magnetoresistive thin film element is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (300) pinned magnetic layer of Co (25)/Cu (20)/Co (10)/NiFe (40)/Ta (30).
A spin-valve magnetoresistive thin film element according to the present invention and a known spin-valve magnetoresistive thin film element were both formed, and subjected to thermal treatment at 260xc2x0 C. for four hours while applying a magnetic field of 200 (Oe).
As can be understood from FIG. 26, the xcex94MR (resistance change rate) of the spin-valve magnetoresistive thin film element according to the present invention is between 7 to 8% at the greatest, and the xcex94MR drops by applying a negative external magnetic field, but the xcex94MR in the present invention drops slower than the xcex94MR of the known spin-valve magnetoresistive thin film element.
Now, with the present invention, the magnitude of the external magnetic field at the time that the xcex94MR is half of the maximum value shall be stipulated as the exchange coupling magnetic field (Hex) generated by the spin-valve magnetoresistive thin film element.
As shown in FIG. 26, the maximum xcex94MR of the known spin valve magnetoresistive thin film element is approximately 8%. Further, the external magnetic field at which the xcex94MR drops to half (the exchange coupling magnetic field (Hex)) is approximately 900 (Oe) absolute value.
In comparison, the maximum xcex94MR of the spin-valve magnetoresistive thin film element according to the present invention is approximately 7.5%, which is slightly lower than the known arrangement, the external magnetic field at which the xcex94MR drops to half (the exchange coupling magnetic field (Hex)) is approximately 2800 (Oe) absolute value, which is much higher.
Thus, it can be understood that the exchange coupling magnetic field (Hex) can be markedly increased with the spin-valve magnetoresistive thin film element according to the present invention wherein the pinned magnetic layer is divided into two layers, as compared with the known spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is formed of one layer, and the stability of the magnetization of the pinned magnetic layer can be improved in comparison with the known arrangement.
Also, the xcex94MR of the present invention does not drop very much as compared with the known arrangement, showing that a high xcex94MR can be maintained.
Also, with the present invention, an antiferromagnetic material which requires thermal treatment is used for generating an exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface between the first pinned magnetic layer and the antiferromagnetic layer, and with the present invention in particular, PtMn alloys are preferably used of all the antiferromagnetic materials which require thermal treatment.
FIG. 27 is a graph showing the relation between environmental temperature and the exchange coupling magnetic field, in cases wherein the antiferromagnetic layer is formed of PtMn, NiO, or FeMn.
The first type of spin-valve magnetoresistive thin film element used is a spin-valve magnetoresistive thin film element according to the present invention wherein a PtMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is divided into two layers. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (200)/first pinned magnetic layer of Co (25)/nonmagnetic intermediate layer of Ru (7)/second pinned magnetic layer of Co (20)/Cu (20)/Co (10)/NiFe (70)/Ta (30).
The second type is a first conventional example wherein a PtMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/antiferromagnetic layer of PtMn (300)/pinned magnetic layer of Co (25)/Cu (25)/Co (10)/NiFe (70)/Ta (30).
The third type is a second conventional example wherein NiO is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/antiferromagnetic layer of NiO (500)/pinned magnetic layer of Co (25)/Cu (25)/Co (10)/NiFe (70)/Ta (30).
The fourth type is a third conventional example wherein an FeMn alloy is used for the antiferromagnetic layer, and the pinned magnetic layer is formed of one layer. The film configuration thereof is from the bottom; the Si substrate/Alumina: Al2O3/Ta (30)/NiFe (70)/Co (10)/Cu (25)/pinned magnetic layer of Co (25)/antiferromagnetic layer of FeMn (150)/Ta (30). In all four types, the numerals in the parentheses represent film thickness in units of xc3xa4ngstrxc3x6m.
The present invention and the first conventional example wherein a PtMn alloy is used for the antiferromagnetic layer are subjected to thermal treatment at 260xc2x0 C. for four hours while applying a magnetic field of 200 (Oe), following formation. The second and third conventional examples wherein NiO and FeMn are used for the antiferromagnetic layer are not subjected to thermal treatment following formation.
As shown in FIG. 27, with the spin-valve magnetoresistive thin film element according to the present invention, the exchange coupling magnetic field (Hex) is approximately 2500 (Oe) under an environment temperature of around 20xc2x0 C., which is very high.
In comparison, with the second conventional example using NiO for the antiferromagnetic layer, and the third conventional example using FeMn for the antiferromagnetic layer, the exchange coupling magnetic field (Hex) is only around 500 (Oe) even under an environment temperature of around 20xc2x0 C., which is low. Also, with the first conventional example using PtMn to form the antiferromagnetic layer, wherein the pinned magnetic layer is formed of a single layer, an exchange coupling magnetic field around 1000 (Oe) is generated under an environment temperature of around 20xc2x0 C., so it can be understood that a greater exchange coupling magnetic field can be obtained than using NiO (second conventional example) or FeMn (third conventional example) for the antiferromagnetic layer.
Japanese Unexamined Patent Publication No. 9-16920 discloses a spin-valve magnetoresistive thin film element which uses NiO for the antiferromagnetic layer, with the pinned magnetic layer being formed of two layers with a nonmagnetic intermediate layer introduced therebetween, and the R-H curve thereof is shown in FIG. 8 of the Patent Publication. According to FIG. 8 of the Patent Publication, an exchange coupling magnetic field (Hex) of 600 (Oe) is then to be obtained, but it can be understood that this is low compared to the exchange coupling magnetic field (around 1000 (Oe), first conventional example) generated wherein a PtMn alloy is used for the antiferromagnetic layer and the pinned magnetic layer is a single layer.
That is to say, in the event that NiO is used for the antiferromagnetic layer, even dividing the pinned magnetic layer into two layers and placing the magnetization of these two layers in a Ferri-state leaves the exchange coupling magnetic field lower than an arrangement wherein a PtMn alloy is used for the antiferromagnetic layer and the pinned magnetic layer is a single layer. Consequently, it can be understood that using the PtMn alloy for the antiferromagnetic layer is preferable from the perspective that a greater exchange coupling magnetic field can be obtained.
Also, as shown in FIG. 27, in the event that NiO or FeMn alloy is used for the antiferromagnetic layer, the exchange coupling magnetic field drops to 0 (Oe) once the environment temperature reaches 200xc2x0 C. This is because the blocking temperature of NiO and FeMn alloys is around 200xc2x0 C., which is low.
Conversely, with the first conventional example wherein the PtMn alloy is used for the antiferromagnetic layer, the exchange coupling magnetic field drops to 0 (Oe) when the environment temperature reaches 400xc2x0 C., so it can be understood that using the PtMn alloy allows the magnetization state of the pinned magnetic layer in an extremely stable condition, temperature-wise.
The blocking temperature is governed by the material used for the antiferromagnetic layer, so with the spin-valve magnetoresistive thin film element according to the present invention shown in FIG. 27, it can be assumed that the exchange coupling magnetic field drops to 0 (Oe) when the environment temperature reaches 400xc2x0 C., but with arrangements which use PtMn alloys as antiferromagnetic layers as with the present invention, blocking temperatures higher than using NiO or the like can be obtained, and further, a very large exchange coupling magnetic field can be obtained during the time taken to reach the blocking temperature by means of dividing the pinned magnetic layer into two layers and placing the magnetization of these two layers in a Ferri-state, so the magnetization state of the two pinned magnetic layers can be maintained in a thermally stable condition.
Also, regarding antiferromagnetic materials which require thermal treatment that can be used instead of PtMn alloys for generating an exchange coupling magnetic field at the interface between the first pinned magnetic layer and the antiferromagnetic layer, the present invention can propose the following: Xxe2x80x94Mn alloys (wherein X is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os), or PtMnxe2x80x94Xxe2x80x2 alloys (wherein Xxe2x80x2 is one or a plurality of the following elements: Pd, Ir, Rh, Ru, Os, Au, Ag).
As described above, with the present invention, the exchange coupling magnetic field (Hex) of the entire spin-valve magnetoresistive thin film element can be increased by means of dividing the pinned magnetic layer into a first pinned magnetic layer and a second pinned magnetic layer with a nonmagnetic intermediate layer introduced therebetween, and by further using an antiferromagnetic material such as a PtMn alloy or the like which exhibits a large exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface with the first pinned magnetic layer, as the antiferromagnetic layer, so the magnetization state of the first pinned magnetic layer and the second pinned magnetic layer can be maintained in a stable antiparallel state (Ferri-state), temperature-wise.
Particularly, with the present invention, the magnitude of magnetic moment at the first pinned magnetic layer and at the second pinned magnetic layer are appropriately controlled, along with controlling the size and direction of the magnetic field applied during thermal treatment, so the magnetization of the first pinned magnetic layer and the second pinned magnetic layer can be maintained in a thermally stable antiparallel state, and the magnetization of the first pinned magnetic layer and the magnetization of the second pinned magnetic layer can be easily directed in the desired direction.